U.S. patent application number 10/644950 was filed with the patent office on 2004-02-26 for active matrix substrate, liquid crystal display panel of transflective type, and liquid crystal display device of transflective type.
Invention is credited to Kanbe, Makoto, Kishimoto, Satoru, Nakamura, Kozo, Tsuda, Kazuhiko.
Application Number | 20040036827 10/644950 |
Document ID | / |
Family ID | 31884632 |
Filed Date | 2004-02-26 |
United States Patent
Application |
20040036827 |
Kind Code |
A1 |
Tsuda, Kazuhiko ; et
al. |
February 26, 2004 |
Active matrix substrate, liquid crystal display panel of
transflective type, and liquid crystal display device of
transflective type
Abstract
A liquid crystal display device of a transflective type of the
present invention is so arranged that a transparent electrode and a
reflective electrode that compose a pixel do not match in position
with each other, and the reflective electrode straddles a gate bus
line and a source bus line. With this, a transparent electrode and
a reflective electrode that are adjacent to each other without
being electrically connected are arranged so as to overlap with
each other, when viewed in the normal direction of the display
surface, thereby eliminating an inter-pixel region therebetween.
This reduces a ratio of the inter-pixel region with respect to the
display screen, so that it is possible to further improve a pixel
aperture ratio and to improve light utilization efficiency.
Inventors: |
Tsuda, Kazuhiko; (Ikoma-gun,
JP) ; Nakamura, Kozo; (Tenri-shi, JP) ; Kanbe,
Makoto; (Sakurai-shi, JP) ; Kishimoto, Satoru;
(Tenri-shi, JP) |
Correspondence
Address: |
NIXON & VANDERHYE, PC
1100 N GLEBE ROAD
8TH FLOOR
ARLINGTON
VA
22201-4714
US
|
Family ID: |
31884632 |
Appl. No.: |
10/644950 |
Filed: |
August 21, 2003 |
Current U.S.
Class: |
349/114 ;
349/158 |
Current CPC
Class: |
G02F 1/133555 20130101;
G02F 1/134336 20130101 |
Class at
Publication: |
349/114 ;
349/158 |
International
Class: |
G02F 001/1335 |
Foreign Application Data
Date |
Code |
Application Number |
Aug 23, 2002 |
JP |
2002-243947 |
Claims
What is claimed is:
1. An active matrix substrate used for a liquid crystal display
device of a transflective type that includes pixel electrodes each
having a reflective electrode and a transparent electrode, wherein:
(i) a reflective electrode and (ii) an adjacent transparent
electrode adjacent to said reflective electrode without being
electrically connected are positioned in such a manner that (A) a
border of a reflection region to which said reflective electrode
applies a voltage and (B) a border of a transmission region to
which said adjacent transparent electrode applies a voltage at
least partly overlap or are closely located with each other, when
viewed in a normal direction of a display surface of said active
matrix substrate.
2. The active matrix substrate as set forth in claim 1, further
comprising: an insulating layer sandwiched between said reflective
electrode and said transparent electrode, said transparent
electrode being on an incident side of light from a light source
and said reflective electrode being on a side of a surface facing a
liquid crystal layer, an edge portion of said reflective electrode
partly superposing an edge portion of said adjacent transparent
electrode adjacent to said reflective electrode without being
electrically connected, when viewed in the normal direction of the
display surface of said active matrix substrate.
3. The active matrix substrate as set forth in claim 2, wherein:
the insulating layer has an opening at a portion corresponding to
said transmission region.
4. The active matrix substrate as set forth in claim 1, further
comprising: a transparent insulating layer sandwiched between (A)
both of said reflective electrode and said transparent electrode
and (B) wiring and a switching element that apply a signal voltage
to said electrodes; and an inter-pixel region between said
reflective electrode and said adjacent transparent electrode
adjacent to said reflective electrode without being electrically
connected, at least part of said inter-pixel region having a width
of not more than 3 .mu.m.
5. The active matrix substrate as set forth in claim 2, wherein:
said reflective electrode does not cover source wiring, when viewed
in the normal direction of the display surface of said active
matrix substrate.
6. The active matrix substrate as set forth in claim 4, wherein:
said reflective electrode does not cover source wiring, when viewed
in the normal direction of the display surface of said active
matrix substrate.
7. The active matrix substrate as set forth in claim 2, wherein:
said reflective electrode covers at least part of gate wiring, when
viewed in the normal direction of the display surface of said
active matrix substrate, and said reflective electrode covers gate
wiring different from gate wiring that drives a pixel of said
reflective electrode.
8. The active matrix substrate as set forth in claim 4, wherein:
said reflective electrode covers at least part of gate wiring, when
viewed in the normal direction of the display surface of said
active matrix substrate, and said reflective electrode covers gate
wiring different from gate wiring that drives a pixel of said
reflective electrode.
9. The active matrix substrate as set forth in claim 2, used for a
liquid crystal display device of the normally white mode, further
comprising: a light-shielding layer located corresponding to a
blank region that is neither said reflection region nor said
transmission region.
10. The active matrix substrate as set forth in claim 4, used for a
liquid crystal display device of the normally white mode, further
comprising: a light-shielding layer located corresponding to a
blank region that is neither said reflection region nor said
transmission region.
11. A liquid crystal display panel of a transflective type that
includes pixel electrodes each having a reflective electrode and a
transparent electrode, further comprising: a counter substrate; an
active matrix substrate, in which (i) a reflective electrode and
(ii) an adjacent transparent electrode adjacent to said reflective
electrode without being electrically connected are positioned in
such a manner that (A) a border of a reflection region to which
said reflective electrode applies a voltage and (B) a border of a
transmission region to which said adjacent transparent electrode
applies a voltage at least partly overlap or are closely located
with each other, when viewed in a normal direction of a display
surface of said active matrix substrate; and a liquid crystal
layer, sandwiched between said counter substrate and said active
matrix substrate.
12. A liquid crystal display device of a transflective type that
includes pixel electrodes each having a reflective electrode and a
transparent electrode, further comprising a liquid crystal display
panel of a transflective type, said panel including: a counter
substrate; an active matrix substrate, in which (i) a reflective
electrode and (ii) an adjacent transparent electrode adjacent to
said reflective electrode without being electrically connected are
positioned in such a manner that (A) a border of a reflection
region to which said reflective electrode applies a voltage and (B)
a border of a transmission region to which said adjacent
transparent electrode applies a voltage at least partly overlap or
are closely located with each other, when viewed in a normal
direction of a display surface of said active matrix substrate; and
a liquid crystal layer, sandwiched between said counter substrate
and said active matrix substrate.
Description
FIELD OF THE INVENTION
[0001] The present invention relates to a liquid crystal panel
structure of a liquid crystal display device of a transflective
type, and in particular to a liquid crystal display device of a
transflective type that has an improved pixel aperture ratio and
realizes light display with excellent light utilization
efficiency.
BACKGROUND OF THE INVENTION
[0002] In these years, application of a liquid crystal display
device to a word processor, a laptop personal computer, a pocket
television, etc. has been rapidly advanced. Among the liquid
crystal display devices, a liquid crystal display device of a
reflection type can show display using ambient light without the
use of a backlight, and consumes a smaller amount of power compared
with a liquid crystal display device of a transmission type. Thus,
the liquid crystal display device of the reflection type has been
recently used for a portable game device, a PDA (Personal Digital
Assistant) device, etc.
[0003] Further, in these years, a liquid crystal display device of
a transflective type has been developed, in which a liquid crystal
display screen can show both reflection display and transmission
display. The liquid crystal display device of the transflective
type can achieve fine display without consuming a large amount of
power by showing the reflection display using ambient light when
the surroundings are bright; and can achieve fine display by
showing the transmission display with turning on a backlight when
the surroundings are dark. Thus, the liquid crystal display device
of the transflective type has come to receive attention
particularly as a display for a cellular phone.
[0004] A conventional liquid crystal display device of the
transflective type generally has a system as shown in Japanese
Unexamined Patent Publication No. 101992/1999 (Tokukaihei
11-101992, published on Apr. 13, 1999; corresponding to U.S. Pat.
No. 6,195,140). The liquid crystal display device disclosed in
Tokukaihei 11-101992 has an arrangement as shown in FIG. 22.
Namely, a plurality of gate bus lines 101 and a plurality of source
bus lines 102 cross with each other, and, in a matrix manner, a
pixel electrode is provided via a switching element (not shown) at
each intersection where the plurality of gate bus lines 101 and the
plurality of source bus lines 102 cross.
[0005] Further, the pixel electrode is composed of a transparent
electrode and a reflective electrode that are electrically
connected with each other. These electrodes are arranged in the
following manner. A transparent insulating layer (not shown) is
formed on the gate bus line 101, the source bus line 102, and the
switching element. On the transparent insulating layer, the
transparent electrode and the reflective electrode are sequentially
formed, allowing a part of the reflective electrode to have an
opening for light transmission. In the liquid crystal display
device, a region where the reflective electrode is formed
(reflection region; shown as the shaded portion in FIG. 22) 103
shows reflection display; while the opening provided in the
reflective electrode (transmission region; shown as the dotted
portion in FIG. 22) 104 shows transmission display.
[0006] However, in the conventional liquid crystal display device
of the transflective type, each pixel area is composed of the
reflection region 103 and the transmission region 104, and each
pixel area is surrounded by an inter-pixel region that insulates
adjacent pixels from one another. The inter-pixel region is formed
in an etching step for forming the transmission and reflection
regions, and thus requires a width of at least about 5 .mu.m.
[0007] Since the inter-pixel region does not contribute to the
screen display, a larger ratio of the inter-pixel region with
respect to the display screen decreases an aperture ratio. In
particular, when a pixel size decreases in a liquid crystal display
panel of high definition, the ratio that the inter-pixel region
occupies the display screen accordingly increases. Thus, in a
liquid crystal display panel used for a cellular phone display,
etc., the inter-pixel region occupies about 20 percent of the
entire display screen, resulting in that the aperture ratio of the
liquid crystal display panel is limited up to about 80 percent.
SUMMARY OF THE INVENTION
[0008] In order to solve the above problems, the present invention
has an object to provide a liquid crystal display device of a
transflective type that has an improved pixel aperture ratio by
reducing an area of an inter-pixel region on a display screen, and
thus has high light utilization efficiency.
[0009] In order to attain the foregoing object, an active matrix
substrate of the present invention, used for a liquid crystal
display device of a transflective type that includes pixel
electrodes each having a reflective electrode and a transparent
electrode, is so arranged that (i) a reflective electrode and (ii)
an adjacent transparent electrode adjacent to the reflective
electrode without being electrically connected are positioned in
such a manner that (A) a border of a reflection region to which the
reflective electrode applies a voltage and (B) a border of a
transmission region to which the adjacent transparent electrode
applies a voltage at least partly overlap or are closely located
with each other, when viewed in a normal direction of a display
surface of the active matrix substrate.
[0010] With this arrangement, a reflective electrode and a
transparent electrode that are adjacent to each other without being
electrically connected are positioned in such a manner that the
border of the reflection region and the border of the transmission
region at least partly overlap (or are closely located) with each
other. This eliminates (or reduces) the inter-pixel region at a
portion where the border of the reflection region and the border of
the transmission region overlap (or are closely located) with each
other.
[0011] With this, in a liquid crystal display panel using the
above-described active matrix substrate, it is possible to reduce a
ratio of the inter-pixel region, which does not contribute to
display, with respect to the entire display screen, thereby
achieving a liquid crystal display panel having a high aperture
ratio.
[0012] Further, a liquid crystal display panel of a transflective
type of the present invention is so arranged that the
above-described active matrix substrate and a counter substrate
sandwich a liquid crystal layer.
[0013] Further, a liquid crystal display device of a transflective
type of the present invention is provided with the above-described
liquid crystal display panel.
[0014] In the above-arranged liquid crystal display panel of the
transflective type and the liquid crystal display device of the
transflective type, as in the above-described active matrix
substrate, it is possible to reduce a ratio of the inter-pixel
region, which does not contribute to display, with respect to the
entire display screen, thereby achieving a high aperture ratio.
[0015] For a fuller understanding of the nature and advantages of
the invention, reference should be made to the ensuing detailed
description taken in conjunction with the accompanying
drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0016] FIG. 1 is a plan view schematically showing an arrangement
of an active matrix substrate of First Embodiment, which shows an
embodiment of the present invention.
[0017] FIG. 2 is a cross-sectional view showing the arrangement of
the active matrix substrate.
[0018] FIG. 3 is a cross-sectional view showing an arrangement of a
liquid crystal display panel using the active matrix substrate.
[0019] FIG. 4(a) is a plan view showing blank regions arising in
the active matrix substrate. FIG. 4(b) is a plan view showing
light-shielding layers provided corresponding to the blank
regions.
[0020] FIG. 5 is a plan view showing another example of the active
matrix substrate of First Embodiment.
[0021] FIG. 6 is a plan view showing a further example of the
active matrix substrate of First Embodiment.
[0022] FIG. 7 is a plan view showing yet another example of the
active matrix substrate of First Embodiment.
[0023] FIG. 8 is a plan view showing still another example of the
active matrix substrate of First Embodiment.
[0024] FIG. 9 is a plan view showing still further another example
of the active matrix substrate of First Embodiment.
[0025] FIG. 10 is a plan view showing yet still another example of
the active matrix substrate of First Embodiment.
[0026] FIG. 11 is a plan view showing a yet further example of the
active matrix substrate of First Embodiment.
[0027] FIG. 12 is a plan view showing a still yet further example
of the active matrix substrate of First Embodiment.
[0028] FIG. 13 is a plan view showing an additional example of the
active matrix substrate of First Embodiment.
[0029] FIG. 14 is a plan view schematically showing an arrangement
of an active matrix substrate of Second Embodiment, which shows
another embodiment of the present invention.
[0030] FIG. 15 is a plan view showing another example of the active
matrix substrate of Second Embodiment.
[0031] FIG. 16 is a plan view schematically showing an arrangement
of an active matrix substrate of Third Embodiment, which shows a
further embodiment of the present invention.
[0032] FIG. 17 is a plan view showing another example of the active
matrix substrate of Third Embodiment.
[0033] FIG. 18 is a plan view showing a further example of the
active matrix substrate of Third Embodiment.
[0034] FIG. 19 is a cross-sectional view schematically showing an
arrangement of an active matrix substrate of Fourth Embodiment,
which shows yet another embodiment of the present invention.
[0035] FIG. 20 is a plan view schematically showing an arrangement
of the active matrix substrate.
[0036] FIGS. 21(a) through 21(j) are cross-sectional views showing
a procedure for manufacturing the active matrix substrate.
[0037] FIG. 22 is a plan view showing an arrangement of a
conventional active matrix substrate used for a liquid crystal
display panel of a transflective type.
DESCRIPTION OF THE EMBODIMENTS
[0038] [First Embodiment]
[0039] The following will explain an embodiment of the present
invention with reference to the drawings.
[0040] First, with reference to FIGS. 1 and 2, explained is an
arrangement of an active matrix substrate used in a liquid crystal
display device of a transflective type in accordance with the
present embodiment.
[0041] An active matrix substrate 1 is so arranged that a gate bus
line (gate wiring) 3, a source bus line (source wiring) 4, and a
TFT (Thin Film Transistor) element 5 as a switching element are
formed on a transparent substrate 2 that is made of glass, etc.
This arrangement is the same with the conventional arrangement, and
thus detailed explanation thereof will be omitted here.
[0042] In the active matrix substrate 1, a pixel electrode is
composed of a transparent electrode 6 and a reflective electrode 7.
The transparent electrode 6 is formed on the transparent substrate
2 via a transparent insulating layer 8, and is connected to the
drain of the TFT element 5. The transparent insulating layer 8 is
formed over an entire display screen area of the active matrix
substrate 1, as an interlayer insulating film between the gate bus
line 3 and the source bus line 4.
[0043] An insulating layer 9 is formed on the gate bus line 3, the
source bus line 4, the TFT element 5, and the transparent electrode
6. Further, the reflective electrode 7 is formed at an upper layer
of the transparent electrode 6 via the insulating layer 9. Further,
the transparent electrode 6 and the reflective electrode 7 are
electrically connected with each other via a contact hole 10
provided in the insulating layer 9.
[0044] Further, an opening 11 is formed in the insulating layer 9
at a portion where the reflective electrode 7 is not formed. The
opening 11, which reveals the transparent electrode 6, becomes a
transmission region for showing transmission display. Note that,
the insulating layer 9 does not always require the opening 11. When
the insulating layer 9 is formed with a transparent insulating
layer, the opening 11 is not required to form the transmission
region. In this case, the transmission region is formed at an upper
portion of the transparent electrode 6 on which the reflective
electrode 7 is not formed.
[0045] On the other hand, the reflective electrode 7 is arranged to
cover the gate bus line 3, the source bus line 4, and the TFT
element 5. Namely, the transparent electrode 6 is placed within
each block area that is separated by the gate bus lines 3 and the
source bus lines 4; while the reflective electrode 7 is placed so
as to extend outside the block area, and to superpose the
transparent electrodes 6 inside adjacent block areas in vertical
and horizontal scanning directions, straddling the gate bus line 3
and the source bus line 4. In other words, the reflective electrode
7 is formed at the upper layer of the transparent electrode 6, but
covers at least part of the inter-pixel region with respect to the
transparent electrode 6, thereby consequently reducing an area that
the inter-pixel region occupies.
[0046] By arranging the transparent electrode 6 and the reflective
electrode 7 in the active matrix substrate 1 as described above, a
boundary of the reflection region (indicated by a shaded portion in
plan views hereinafter) overlaps a boundary of the transmission
region (indicated by a dotted portion in plan views hereinafter)
almost all around the pixel electrode, as shown in FIG. 1, when the
planar surface of the active matrix substrate 1 is viewed in a
direction of the normal line. The inter-pixel region does not arise
where the reflection region overlaps the transmission region,
thereby remarkably improving an aperture ratio of a liquid crystal
display panel using the active matrix substrate 1.
[0047] FIG. 3 is a cross-sectional view of a liquid crystal display
panel of a transflective type that is manufactured using the active
matrix substrate 1.
[0048] The liquid crystal display panel has an arrangement such
that an active matrix substrate 1' and a counter substrate 21
sandwich a liquid crystal layer 31. Note that, the active matrix
substrate 1' in FIG. 3 is so arranged that a retardation film 12
and a polarizer 13 are provided on the active matrix substrate 1 in
FIG. 2 on the opposite side from a surface facing the liquid
crystal layer 31. Further, the counter substrate 21 is so arranged
that a color filter 23 and a counter electrode 24 are provided on a
glass substrate 22 on a surface facing the liquid crystal layer 31,
and a retardation film 25 and a polarizer 26 are provided on the
glass substrate 22 on the opposite surface.
[0049] In the liquid crystal display panel as arranged above, a
voltage (namely, data signal) supplied from the gate bus line 4 is
applied to the transparent electrode 6 via the TFT element 5, and
then applied via the contact hole 10 to the reflective electrode 7
on the insulating layer 9. With this, (A) either the transparent
electrode 6 or the reflective electrode 7 on the active matrix
substrate 1' and (B) the counter electrode 24 on the counter
substrate 21 generate a potential difference, and the liquid
crystal layer 31 is driven by the potential difference.
[0050] Further, the liquid crystal display panel is so arranged
that, in the active matrix substrate 1', the insulating layer 9 has
the opening 11. In this arrangement, the transmission region and
the reflection region may have different cell thicknesses of the
liquid crystal layer 31 so that the transmission region has the
cell thickness more than the reflection region by a thickness of
the insulating layer 9. This arrangement is preferable because
retardation changes of the liquid crystal layer 31 upon the voltage
application can be reduced. Further, when the cell thickness of the
transmission region is twice as that of the reflection region, a
light path length of light in the reflection region (through which
light passes twice when back and forth) becomes equal to a light
path length of light in the transmission region (through which
light passes once in one direction). This arrangement is most
preferable because the same optical changes are achieved all over
the liquid crystal layer 31 in response to the voltage
application.
[0051] Here, in the liquid crystal display panel having the
arrangement shown in FIG. 1, when a pixel pitch is 270 .mu.m in
height and 90 .mu.m in width, and a width between the reflective
electrodes and a width between the transparent electrodes are both
7 .mu.m, for example, the aperture ratio is calculated as follows:
the aperture ratio of the reflection region is 89.8%, the aperture
ratio of the transmission region is 8.9%, and the total aperture
ratio is 98.7%. Namely, it is possible to realize a liquid crystal
display panel of the transflective type having excellent light
utilization efficiency.
[0052] As described above, in the liquid crystal display panel
having the above arrangement, most of the display screen can
contribute to display as either the transmission region or the
reflection region. However, between adjacent reflective electrodes
7 and between adjacent transparent electrodes 6, there remains a
small area of inter-pixel region that does not contribute to
display, as shown in FIG. 4(a). Further, the gate bus line 3 or the
source bus line 4 is located in the inter-pixel region, and there
remains a certain area of blank region 14 between (A) the gate bus
line 3 or the source bus line 4 and (B) the transparent electrode
6.
[0053] Namely, even in the active matrix substrate 1 which
eliminates the inter-pixel region in each pixel electrode composed
of the transparent electrode 6 and the reflective electrode 7, the
inter-pixel region in a grid manner still exists between the
transparent electrodes 6 and between the reflective electrodes 7.
Further, where the inter-pixel region of the transparent electrodes
6 and the inter-region of the reflective electrodes 7 cross, there
is the blank region 14 to which neither the transparent electrode 6
nor the reflective electrode 7 can apply a voltage.
[0054] The blank region 14 cannot apply a voltage to the liquid
crystal layer 31. Thus, when a substrate corresponding to the blank
region 14 transmits light, the blank region 14 always shows white
display in the normally white mode, thus decreasing the
contrast.
[0055] Therefore, in a liquid crystal display panel of the normally
white mode, as shown in FIG. 4(b), a light-shielding layer 15
corresponding to the blank region 14 needs to be provided at a
layer different from the transparent electrode 6 and the reflective
electrode 7. The light-shielding layer 15 is preferably formed in a
step of forming the gate bus line 3 or the source bus line 4,
without an additional step (FIG. 4(b) shows a case where the
light-shielding layer 15 is formed in the step of forming the gate
bus line 3). Incidentally, the light-shielding layer 15 is not
required in the normally black mode where the blank region 14
always shows black display.
[0056] Note that, the present embodiment has been explained an
example which aims to obtain an area of the reflective electrode 7
as large as possible. However, a ratio of the reflection region to
the transmission region is not limited to this. In other words, the
transparent electrode 6 and the reflective electrode 7 can be set
to have any shape and area. FIGS. 5 through 13 will show variant
examples.
[0057] Each of the arrangements shown in FIGS. 5 through 13 is such
that the reflective electrode 7 covers both the gate bus line 3 and
the source bus line 4. Note that, in FIGS. 5 through 13,
illustration of some members such as an electrode and wiring are
omitted to clearly show the shape of the transparent electrode 6,
the position where the TFT element 5 connects the transparent
electrode 6, etc.
[0058] The shape of the reflective electrode 7 is not limited, and
may be varied in many ways. The reflective electrode 7 may have a
substantial "L" shape as shown in FIG. 5, a substantial "T" shape
as shown in FIGS. 6 and 7, a substantial "+" shape as shown in
FIGS. 8 through 11, a rectangular shape as shown in FIGS. 12 and
13, etc.
[0059] Further, in the conventional liquid crystal display panel of
the transflective type, the gate bus line and the source bus line
are located in the inter-pixel region. Thus, each of the bus lines
is designed to have a width as narrow as possible, because an
aperture ratio of the liquid crystal display panel decreases as
each of the bus lines becomes wider.
[0060] In contrast, in the liquid crystal display panel in
accordance with the present embodiment, the gate bus line 3 and the
source bus line 4 are covered with the reflective electrode 7, and
most of the line areas are used as the reflection region. Thus,
even when the gate bus line 3 and the source bus line 4 become
wider, this is not likely to decrease the aperture ratio.
Therefore, in particular, by forming the gate bus line 3 wider to
decrease the line resistance, as shown in FIGS. 5 through 13, it is
possible to reduce bad effects such as signal delay due to the line
resistance.
[0061] Further, in the arrangement in which the gate bus line 3 is
formed wider, the transparent electrodes 6 on both sides of the
gate bus line 3 may be arranged so that an edge portion of each of
the transparent electrodes 6 superposes the gate bus line 3 in
question (Namely, the inter-pixel region of adjacent transparent
electrodes 6 that sandwich the gate bus line 3 rests on the gate
bus line 3 in question), thereby eliminating the blank regions 14
on both sides of the gate bus line 3.
[0062] Further, each of the liquid crystal display panels shown in
FIGS. 5 through 13 is provided with the light-shielding layer 15.
The light-shielding layer 15 may be provided in any island shape
corresponding to a portion to be shielded (namely, corresponding to
the blank region 14).
[0063] Further, to increase the ratio of the transmission region in
the liquid crystal display device of the transflective type in
accordance with the present embodiment, it is most preferable that
the reflective electrode 7, which has a rectangular shape, is
arranged so as to cover each portion where the inter-pixel region
extending in the vertical scanning direction between the
transparent electrodes 6 and the inter-pixel region extending in
the horizontal scanning direction between the transparent
electrodes 6 cross, as shown in FIGS. 12 and 13. This is because
the reflective electrode 7 can cover a larger ratio of the
inter-pixel region with respect to the transparent electrodes
6.
[0064] [Second Embodiment]
[0065] The following will explain another embodiment of the present
invention, with reference to the drawings.
[0066] First Embodiment has an arrangement in which the reflective
electrode 7 covers the inter-pixel region of the transparent
electrodes 6 with respect to both vertical and horizontal scanning
directions. However, in the liquid crystal display device of the
transflective type of the present invention, the reflective
electrode 7 may cover the inter-pixel region of the transparent
electrodes 6 with respect to at least one of the vertical and
horizontal scanning directions. The present embodiment has an
arrangement in which the reflective electrode 7 only covers the
inter-pixel region extending in the horizontal scanning direction
between the transparent electrodes 6.
[0067] An arrangement of an active matrix substrate used in a
liquid crystal display device of the transflective type in
accordance with the present embodiment will be explained with
reference to FIG. 14. FIG. 14 shows an arrangement in which the
reflective electrode 7 covers only the gate bus line 3 and the TFT
element 5, and does not cover the source bus line 4. Note that, in
FIG. 14, illustration of some members such as an electrode and
wiring are omitted to clearly show the shape of the transparent
electrode 6, the position where the TFT element 5 connects the
transparent electrode 6, etc.
[0068] The liquid crystal display panel using the active matrix
substrate having the arrangement shown in FIG. 14 is less
advantageous than the liquid crystal display panel of First
Embodiment in terms of the aperture ratio, because the reflective
electrode 7 does not cover the source bus line 4. However, this
liquid crystal display panel reduces a parasitic capacitance
between the source bus line 4 and the pixel electrode (the
reflective electrode 7, in particular). Thus, in a TFT liquid
crystal display panel having a diagonal length of not less than
about 10 cm, in particular, this arrangement is effective to reduce
crosstalk (shadow) caused by capacitive coupling of the source bus
line 4 and the pixel electrode.
[0069] Further, in the active matrix substrate shown in FIG. 14,
the reflective electrode 7 covers the gate bus line 3. This
eliminates the inter-pixel region extending in the horizontal
scanning direction between the transparent electrodes 6, thereby
improving the aperture ratio. Here, each of the reflective
electrodes 7 is arranged to cover a gate bus line 3 which is one
line above the gate bus line 3 that drives the pixel of the
reflective electrode 7 in question. Namely, the reflective
electrode 7 is arranged to cover a gate bus line 3 different from
the gate bus line 3 that drives the pixel of the reflective
electrode 7 in question.
[0070] When the reflective electrode 7 is arranged to cover the
gate bus line 3 that drives the pixel of the reflective electrode 7
in question, the parasitic capacitance between the reflective
electrode 7 and the gate bus line 3 increases. This accordingly
increases a change in a pixel potential when the gate signal falls
after writing, resulting in a display defect. Note that, also in
the arrangement of First Embodiment, it is preferable that the
reflective electrode 7 covers a gate bus line 3 different from the
gate bus line 3 that drives the pixel of the reflective electrode 7
in question, when each of the reflective electrodes 7 covers the
gate bus line 3.
[0071] When the above-described problem is negligible, the present
invention of course includes an arrangement in which the reflective
electrode 7 covers the gate bus line 3 of the pixel of the
reflective electrode 7 in question.
[0072] Here, in the liquid crystal display panel having the
arrangement shown in FIG. 14, when a pixel pitch is 270 .mu.m in
height and 90 .mu.m in width, and a width between the reflective
electrodes and a width between the transparent electrodes are both
7 .mu.m, for example, the aperture ratio is calculated as follows:
the aperture ratio of the reflection region is 89.7%, the aperture
ratio of the transmission region is 2.4%, and the total aperture
ratio is 92.2%. Namely, it is possible to realize a liquid crystal
display panel of the transflective type having excellent light
utilization efficiency.
[0073] Note that, the present embodiment has been explained an
example which aims to obtain an area of the reflective electrode 7
as large as possible. However, a ratio of the reflection region to
the transmission region is not limited to this. In other words, the
transparent electrode 6 and the reflective electrode 7 can be set
to have any shape and area. For example, as shown in FIG. 15, by
designing the shape and area of the reflective electrode 7
variously, it is possible to desirably set a ratio of the
reflection region to the transmission region.
[0074] [Third Embodiment]
[0075] The following will explain a further embodiment of the
present invention, with reference to the drawings.
[0076] First Embodiment has an arrangement in which the reflective
electrode 7 covers the inter-pixel region of the transparent
electrodes 6 with respect to both vertical and horizontal scanning
directions. However, in the liquid crystal display device of the
transflective type of the present invention, the reflective
electrode 7 may cover the inter-pixel region of the transparent
electrodes 6 with respect to at least one of the vertical and
horizontal scanning directions. The present embodiment has an
arrangement in which the reflective electrode 7 only covers the
inter-pixel region extending in the vertical scanning direction
between the transparent electrodes 6.
[0077] An arrangement of an active matrix substrate used in a
liquid crystal display device of the transflective type in
accordance with the present embodiment will be explained with
reference to FIG. 16. FIG. 16 shows an arrangement in which the
reflective electrode 7 covers only the source bus line 4 and the
TFT element 5, and does not cover the gate bus line 3. Note that,
in FIG. 16, illustration of some members such as an electrode and
wiring are omitted to clearly show the shape of the transparent
electrode 6, the position where the TFT element 5 connects the
transparent electrode 6, etc.
[0078] The liquid crystal display panel using the active matrix
substrate having the arrangement shown in FIG. 16 is less
advantageous than the liquid crystal display panel of First
Embodiment in terms of the aperture ratio, because the reflective
electrode 7 does not cover the gate bus line 3. However, this
liquid crystal display panel is effective for employing a structure
to reduce flicker in which the TFT elements 5 are arranged in a
zigzag manner with respect to the gate bus line, for example.
[0079] When the TFT elements 5 are arranged in a zigzag manner with
respect to the gate bus line 3, if the reflective electrode 7
covers the gate bus line 3, the reflective electrode 7 covers a
portion of the gate bus line 3 that drives the pixel of the
reflective electrode 7 in question. Namely, as shown in FIG. 16,
when the TFT elements 5 are arranged in a zigzag manner with
respect to the gate bus line 3, if the reflective electrodes 7 are
linearly arranged to cover the gate bus line 3, the reflective
electrode 7 covers the gate bus line 3 that drives the pixel of the
reflective electrode 7 in question, on either the column where the
TFT elements 5 are arranged below the gate bus line 3 or the column
where the TFT elements 5 are arranged above the gate bus line 3.
When the reflective electrode 7 covers the gate bus line 3 that
drives the pixel of the reflective electrode 7 in question, the
parasitic capacitance between the reflective electrode 7 and the
gate bus line 3 increases. This accordingly increases a change in a
pixel potential when the gate signal falls after writing, resulting
in a display defect.
[0080] Therefore, in the active matrix substrate shown in FIG. 16,
the reflective electrode 7 covers the source bus line 4 so as to
eliminate the inter-pixel region extending in a vertical scanning
direction between the transparent electrodes 6, thereby improving
the aperture ratio; and the reflective electrode 7 does not cover
the gate bus line 3, thereby showing fine display.
[0081] Further, in the arrangement in which the TFT elements 5 are
arranged in a zigzag manner with respect to the gate bus line 3, by
arranging the reflective electrodes 7 on the same column to shift
in the vertical scanning direction, the reflective electrode 7 can
cover a gate bus line 3 rather than the gate bus line 3 that drives
the pixel of the reflective electrode 7 in question. However, in
this arrangement, the reflective electrodes 7 on the same column
are arranged in a zigzag manner, and may thus cause a problem such
as line blurring when displaying a straight line.
[0082] Here, in the liquid crystal display panel having the
arrangement shown in FIG. 16, when a pixel pitch is 270 .mu.m in
height and 90 .mu.m in width, and a width between the reflective
electrodes and a width between the transparent electrodes are both
7 .mu.m, for example, the aperture ratio is calculated as follows:
the aperture ratio of the reflection region is 89.8%, the aperture
ratio of the transmission region is 7.3%, and the total aperture
ratio is 97.1%. Namely, it is possible to realize a liquid crystal
display panel of the transflective type having excellent light
utilization efficiency.
[0083] Note that, the present embodiment has been explained an
example which aims to obtain an area of the reflective electrode 7
as large as possible. However, a ratio of the reflection region to
the transmission region is not limited to this. In other words, the
transparent electrode 6 and the reflective electrode 7 can be set
to have any shape and area. For example, as shown in FIGS. 17 and
18, by designing the shape and area of the reflective electrode 7
variously, it is possible to desirably set a ratio of the
reflection region to the transmission region. Further, in the
arrangement in which the reflective electrode 7 covers the source
bus line 4, the reflective electrode may cover the source bus line
4 connected with the pixel of the reflective electrode 7 in
question, or may cover any other source bus line 4.
[0084] [Fourth Embodiment]
[0085] The following will explain yet another embodiment of the
present invention with reference to the drawings.
[0086] First through Third Embodiments are arranged so that the
reflection region overlaps the transmission region at least part of
the circumference of the pixel electrode, and thus the overlapping
portion eliminates the inter-pixel region so as to improve the
aperture ratio. However, the present invention is not limited to
this. Even when there is the inter-pixel region, the aperture ratio
can be improved by narrowing the inter-pixel region compared with
the conventional arrangement. Such an arrangement will be explained
in the present embodiment.
[0087] An arrangement of an active matrix substrate used in a
liquid crystal display device of a transflective type in accordance
with the present embodiment will be explained with reference to
FIGS. 19 and 20.
[0088] An active matrix substrate 51 is so arranged that the gate
bus line 3, the source bus line 4, and the TFT element 5 as the
switching element are formed on the transparent substrate 2 such as
glass. Like the arrangement of First Embodiment, the arrangement
thus far is the same with the conventional arrangement, thus their
detailed explanation will be omitted here.
[0089] The drain of the TFT element 5 is connected with a
connecting electrode 52, over which a transparent insulating layer
53 is formed. The transparent insulating layer 53 has a contact
hole 54 at a portion corresponding to the connecting electrode 52.
The connecting electrode 52 and the pixel electrode are connected
with each other via the contact hole 54.
[0090] In the active matrix substrate 51 in accordance with the
present embodiment, the pixel electrode is composed of the
transparent electrode 6 and the reflective electrode 7. However, in
the active matrix substrate 51, an insulating layer is not provided
between the transparent electrode 6 and the reflective electrode 7.
Instead, both of the transparent electrode 6 and the reflective
electrode 7 are formed almost at the same layer on the transparent
insulating layer 53.
[0091] Further, in the active matrix substrate 51, both of the
transparent electrode 6 and the reflective electrode 7 are formed
almost at the same layer on the transparent insulating layer 53.
Thus, it is required to provide the inter-pixel region between the
transparent electrode 6 and the reflective electrode 7 so as to
insulate adjacent pixels from one another.
[0092] In the active matrix substrate 51 as arranged above,
however, a width of the inter-pixel region between the transparent
electrode 6 and the reflective electrode 7 can be set in accordance
with the positioning when the transparent electrode 6 and the
reflective electrode 7 are patterned. In other words, the width is
not limited by the etching. Thus, in the active matrix substrate
51, it is possible to form a sufficiently narrower inter-pixel
region between the transparent electrode 6 and the reflective
electrode 7, compared with the conventional arrangement. Therefore,
it is possible to reduce the inter-pixel region to so as improve
the aperture ratio.
[0093] The following will explain a procedure for manufacturing the
active matrix substrate 51 as described above, with reference to
FIGS. 21(a) through 21(j).
[0094] FIG. 21(a) shows a state where the gate bus line 3, the
source bus line 4, the TFT element 5, and the connecting electrode
52 are formed on the transparent substrate 2. Over this state,
photosensitive acrylic resin is applied to form the transparent
insulating layer 53, as shown in FIG. 21(b), which is then exposed
using a photomask 61, as shown in FIG. 21(c). Following this, after
undergoing developing and heating steps, the contact hole 54 is
formed in the transparent insulating layer 53, as shown in FIG.
21(d).
[0095] Here, the transparent insulating layer 53 may have an uneven
surface on a portion except the contact hole 54 (see FIG. 19). The
uneven surface can be formed in such a manner that, using a
photomask having a predetermined shape, the transparent insulating
layer 53 is exposed with light having illuminance lower than the
portion of the contact hole, and is then subjected to developing
and heating steps. Alternatively, instead of the photosensitive
acrylic resin, a dry film resist having an uneven surface may be
pasted on by a laminating process in the initial state to form the
transparent insulating layer 53. This uneven surface is preferable,
particularly when formed on the reflection region, because the
reflective electrode 7 formed on the uneven surface can utilize
reflected light as diffused reflection.
[0096] Next, as shown in FIG. 21(e), a transparent electrode
material is formed into a film over the active matrix substrate 51
in which the contact hole 54 is formed in the transparent
insulating layer 53. Further, as shown in FIGS. 21(f) and 21(g),
the transparent electrode 6 having a predetermined shape is
patterned through patterning steps (deposition, photo (exposing),
etching (developing)) using a resist 62 and a photomask 63.
[0097] Next, as shown in FIG. 21(h), a reflective electrode
material is formed into a film. Further, as shown in FIGS. 21(i)
and 21(j), the reflective electrode 7 having a predetermined shape
is patterned through patterning steps (deposition, photo
(exposing), etching (developing)) using a resist 64 and a photomask
65.
[0098] Here, the photomasks 63 and 65, which are used for
patterning the transparent electrode 6 and the reflective electrode
7 respectively, can be adjusted in accordance with positioning
accuracy of approximately 1 .mu.m. Thus, as shown in FIG. 21(j), as
for adjacent transparent electrode 6 and reflective electrode 7
that sandwich an inter-pixel region 66, the width of the
inter-pixel region 66 can be adjusted to not more than 3 .mu.m
including side shift due to overetching of the transparent
electrode 6 and the reflective electrode 7.
[0099] Thus, in the active matrix substrate 51, the inter-pixel
region can be formed narrower than the conventional liquid crystal
display panel in which the inter-pixel region is formed by etching
(a width of not less than 5 .mu.m is usually required to surely
separate adjacent pixels from one another). Therefore, it is
possible to realize a liquid crystal display panel having a high
aperture ratio by reducing an area of the inter-pixel region.
[0100] The liquid crystal display panel having the arrangement in
accordance with the present embodiment has beneficial features as
described below.
[0101] Each of the arrangements of First through Third Embodiments
has a double-story structure of the transparent electrode 6 and the
reflective electrode 7 via the insulating layer 9. Further, in
order to allow the transmission region and the reflection region to
have the equal retardation value, the transparent electrode 6 is
provided at a lower layer of the insulating layer 9, and the
insulating layer 9 has the opening 11 at a portion corresponding to
the transmission region (see FIG. 2).
[0102] In this structure, a sidewall portion of the opening 11 is
not actually parallel to the normal direction of the display
surface. Namely, the sidewall portion has a steep inclination over
a certain amount of area. When Al as the reflective electrode 7 is
provided on the inclined surface, light incident from above is
reflected at a large degree on the steeply inclined surface and
thus confined in the cell. Because of this, an area that does not
contribute to display arises on the inclined portion, namely at the
boundary portion between the reflection region and the transmission
region.
[0103] The arrangement of the present embodiment achieves a
multigap structure of the reflection region and the transmission
region by providing a protrusion on the counter substrate (CF
substrate) 21 side. This eliminates the inclined portion at the
boundary of the reflection region and the transmission region,
thereby preventing the reflective electrode 7 to be placed on the
steeply inclined portion. Namely, the arrangement of the present
embodiment cannot completely eliminate the inter-pixel region
compared with the arrangements in First through Third Embodiments,
but does not cause a problem such that the inclined portion
decreases the display area. Of course, the area that does not
contribute to display on the inclined portion is sufficiently
smaller than the conventional inter-pixel region, but the
arrangement of the present embodiment may achieve a higher aperture
ratio than the arrangements in First through Third Embodiments,
depending on design conditions.
[0104] Incidentally, in the active matrix substrate 51 shown in
FIG. 19, the reflective electrode 7 is connected to the connecting
electrode 52 via the contact hole 54, but the transparent 6 may be
connected to the connecting electrode 52, as shown in FIG. 20. Note
that, when the transparent electrode 6 is connected to the
connecting electrode 52, the transparent electrode 6 is placed on
the connecting electrode 52. Thus, the connecting electrode 52
needs to be formed with a transparent conductive film to prevent
the lowering of the aperture ratio.
[0105] Further, in the active matrix substrate 51, the reflective
electrode 7 may be formed to cover at least one of the gate bus
line 3 and the source bus line 4. The achievable effects in this
case are the same with those explained in Second and Third
Embodiments.
[0106] Further, the active matrix substrate 51 in accordance with
the present embodiment is preferably arranged so that, when the
reflective electrode 7 covers the gate bus line 3, the reflective
electrode 7 covers a gate bus line 3 different from the gate bus
line 3 that drives the pixel of the reflective electrode 7 in
question, as in First and Second Embodiments.
[0107] Further, when a liquid crystal display device of a
transflective type using the active matrix substrate 51 is driven
by the normally white mode, the contrast decrease can be prevented
by providing the light-shielding layer on the blank region that is
neither the reflection region nor the transmission region, as
explained in First Embodiment.
[0108] Further, a liquid crystal display panel is composed in such
a manner that the active matrix substrate 51 in accordance with the
present embodiment and the counter substrate sandwich the liquid
crystal layer. Here, the transparent electrode 6 and the reflective
electrode 7 are formed almost at the same layer in the active
matrix substrate 51. Thus, it is preferable that, in the counter
electrode on the side of the counter substrate, the transmission
region and the reflection region have different thicknesses, so as
to reduce a difference in light path length between light passing
through the reflection region and light passing through the
transmission region. With this, retardation changes of the liquid
crystal layer upon the voltage application become similar in the
reflection region and the transmission region, thereby achieving
fine display.
[0109] Further, a liquid crystal display device of a transflective
type is composed in such a manner that a driving circuit, a light
source 41 (see FIG. 3), etc. are mounted on each of the liquid
crystal display panels explained in First through Fourth
Embodiments.
[0110] As described above, an active matrix substrate in accordance
with First through Fourth Embodiments, which includes pixel
electrodes each having a reflective electrode 7 and a transparent
electrode 6, is so arranged that (i) a reflective electrode 7 and
(ii) an adjacent transparent electrode 6 adjacent to the reflective
electrode without being electrically connected are positioned in
such a manner that (A) a border of a reflection region to which the
reflective electrode 7 applies a voltage and (B) a border of a
transmission region to which the adjacent transparent electrode 6
applies a voltage at least partly overlap (First through Third
Embodiments) or are closely located (Fourth Embodiment) with each
other, when viewed in a normal direction of a display surface of
the active matrix substrate.
[0111] With this arrangement, a reflective electrode 7 and a
transparent electrode 6 that are adjacent to each other without
being electrically connected are positioned in such a manner that
the border of the reflection region and the border of the
transmission region at least partly overlap (or are closely
located) with each other. This eliminates (or reduces) the
inter-pixel region at a portion where the border of the reflection
region and the border of the transmission region overlap (or are
closely located) with each other.
[0112] With this, in a liquid crystal display panel using the
above-described active matrix substrate, it is possible to reduce a
ratio of the inter-pixel region, which does not contribute to
display, with respect to the entire display screen, thereby
achieving a liquid crystal display panel having a high aperture
ratio.
[0113] Further, the active matrix substrate in accordance with
First through Third Embodiments is provided with a plurality of
gate bus lines 3 and a plurality of source bus lines 4 that cross
with each other; a TFT element 5 provided at each intersection
where the plurality of gate bus lines 3 and the plurality of source
bus lines 4 cross; and a pixel electrode connected to the TFT
element 5 and composed of the transparent electrode 6 and the
reflective electrode 7. Then, the reflective electrode 7 and the
transparent electrode 6 sandwich an insulating layer 9, so that the
transparent electrode 6 is on an incident side of light from a
light source and the reflective electrode 7 is on a side of a
surface facing a liquid crystal layer. Further, the reflective
electrode 7 is arranged on the insulating layer 9 so as to straddle
at least one of the gate bus line 3 and the source bus line 4.
Namely, an edge portion of the reflective electrode 7 partly
superposes an edge portion of the adjacent transparent electrode 6
that is adjacent to the reflective electrode 7 without being
electrically connected, when viewed in the normal direction of the
display surface of the active matrix substrate.
[0114] In the above-arranged active matrix substrate, an edge
portion of the reflective electrode 7 partly superposes an edge
portion of the adjacent transparent electrode 6 that is adjacent to
the reflective electrode 7 without being electrically connected, so
that the reflection region and the transmission region overlap with
each other when viewed in the normal direction of the display
surface of the active matrix substrate.
[0115] With this, the inter-pixel region is completely eliminated
at the portion where the reflection region and the transmission
region overlap. Namely, in a liquid crystal display panel using the
above-described active matrix substrate, it is possible to achieve
a high aperture ratio. Further, the reflective electrode 7 and the
transparent electrode 6 that overlap with each other can be
electrically insulated with each other by sandwiching the
insulating layer 9 therebetween.
[0116] Further, the active matrix substrate in accordance with
Fourth Embodiment is provided with a plurality of gate bus lines 3
and a plurality of source bus lines 4 that cross with each other; a
TFT element 5 provided at each intersection where the plurality of
gate bus lines 3 and the plurality of source bus lines 4 cross; and
a pixel electrode connected to the TFT element 5 and composed of
the transparent electrode 6 and the reflective electrode 7.
[0117] Then, both of the reflective electrode 7 and the transparent
electrode 6 are formed to sandwich a transparent insulating layer
53 with respect to the gate bus line 3, the source bus line 4, and
the TFT element 5, and an inter-pixel region between the reflective
electrode 7 and the adjacent transparent electrode 6 that are
adjacent to each other without being electrically connected is at
least partly formed to have a width of not more than 3 .mu.m.
[0118] In the above-described active matrix substrate, both of the
reflective electrode 7 and the transparent electrode 6 are formed
almost at the same layer on the transparent insulating layer 53.
Thus, it is required to provide the inter-pixel region for
insulation between the electrodes of different pixels.
[0119] Here, the inter-pixel region formed between the same type of
electrodes (namely, between the reflective electrodes 7 or between
the transparent electrodes 6) generally requires a width of at
least not less than 5 .mu.m, in accordance with etching accuracy.
In contrast, the inter-pixel region between the different types of
electrodes (namely between the reflective electrode 7 and the
transparent electrode 6) can be adjusted in accordance with the
positioning accuracy when the pattern is formed. Thus, it becomes
possible to form a sufficiently narrow (not more than 3 .mu.m)
inter-pixel region compared with the conventional inter-pixel
region between the same type of electrodes.
[0120] Therefore, the inter-pixel region between the reflective
electrode 7 and the adjacent transparent electrode 6 adjacent to
the reflective electrode 7 without being electrically connected is
at least partly formed to have a width of not more than 3 .mu.m,
thereby reducing the inter-pixel region that does not contribute to
display. Namely, it is possible to attain a high aperture ratio in
a liquid crystal display panel using the above-described active
matrix substrate.
[0121] As described above, an active matrix substrate of the
present invention, used for a liquid crystal display device of a
transflective type that includes pixel electrodes each having a
reflective electrode and a transparent electrode, is so arranged
that (i) a reflective electrode and (ii) an adjacent transparent
electrode adjacent to the reflective electrode without being
electrically connected are positioned in such a manner that (A) a
border of a reflection region to which the reflective electrode
applies a voltage and (B) a border of a transmission region to
which the adjacent transparent electrode applies a voltage at least
partly overlap or are closely located with each other, when viewed
in a normal direction of a display surface of the active matrix
substrate.
[0122] With this arrangement, a reflective electrode and a
transparent electrode that are adjacent to each other without being
electrically connected are positioned in such a manner that the
border of the reflection region and the border of the transmission
region at least partly overlap (or are closely located) with each
other. This eliminates (or reduces) the inter-pixel region at a
portion where the border of the reflection region and the border of
the transmission region overlap (or are closely located) with each
other.
[0123] With this, in a liquid crystal display panel using the
above-described active matrix substrate, it is possible to reduce a
ratio of the inter-pixel region, which does not contribute to
display, with respect to the entire display screen, thereby
achieving a liquid crystal display panel having a high aperture
ratio.
[0124] Further, the active matrix substrate of the present
invention may be arranged so as to include an insulating layer
sandwiched between the reflective electrode and the transparent
electrode, the transparent electrode being on an incident side of
light from a light source and the reflective electrode being on a
side of a surface facing a liquid crystal layer; an edge portion of
the reflective electrode partly superposing an edge portion of the
adjacent transparent electrode adjacent to the reflective electrode
without being electrically connected, when viewed in the normal
direction of the display surface of the active matrix
substrate.
[0125] With this arrangement, an edge portion of the reflective
electrode partly superposes an edge portion of the adjacent
transparent electrode that is adjacent to the reflective electrode
without being electrically connected, so that the reflection region
and the transmission region overlap with each other when viewed in
the normal direction of the display surface of the active matrix
substrate.
[0126] With this, the inter-pixel region is completely eliminated
at the portion where the reflection region and the transmission
region overlap with each other. Namely, in a liquid crystal display
panel using the above-described active matrix substrate, it is
possible to achieve a high aperture ratio. Further, the reflective
electrode and the transparent electrode that overlap with each
other can be electrically insulated with each other by sandwiching
the insulating layer therebetween.
[0127] Further, the active matrix substrate of the present
invention is preferably arranged so that the insulating layer has
an opening at a portion corresponding to the transmission
region.
[0128] In the arrangement where the insulating layer is provided
between the reflective electrode and the transparent electrode, in
order to form the transmission region using a region where the
reflective electrode is not formed, the insulating layer may be
transparent; or the insulating layer may have the opening at the
transmission region.
[0129] With the above-mentioned arrangement, the insulating layer
has the opening at a portion corresponding to the transmission
region. With this, in a liquid crystal display panel using the
above-described active matrix substrate, the transmission region
and the reflection region can have different cell thicknesses of
the liquid crystal layer so that the transmission region has the
cell thickness more than the reflection region by a thickness of
the insulating layer. In this case, retardation changes of the
liquid crystal layer upon the voltage application can be similar in
the reflection region and the transmission region, thereby
achieving fine display.
[0130] Further, the active matrix substrate of the present
invention may be arranged so as to include a transparent insulating
layer sandwiched between (A) both of the reflective electrode and
the transparent electrode and (B) wiring and a switching element
that apply a signal voltage to the electrodes; and an inter-pixel
region between the reflective electrode and the adjacent
transparent electrode adjacent to the reflective electrode without
being electrically connected, at least part of the inter-pixel
region having a width of not more than 3 .mu.m.
[0131] With this arrangement, both of the reflective electrode and
the transparent electrode are formed almost at the same layer on
the transparent insulating layer. Thus, it is required to provide
the inter-pixel region for insulation between the electrodes of
different pixels.
[0132] Here, the inter-pixel region formed between the same type of
electrodes (namely, between the reflective electrodes or between
the transparent electrodes) generally requires a width of at least
not less than 5 .mu.m, depending on etching accuracy. In contrast,
the inter-pixel region between the different types of electrodes
(namely between the reflective electrode and the transparent
electrode) can be adjusted with the positioning accuracy when the
pattern is formed. Thus, it becomes possible to form a sufficiently
narrow (not more than 3 .mu.m) inter-pixel region compared with the
conventional inter-pixel region between the same type of
electrodes.
[0133] Therefore, the inter-pixel region between the reflective
electrode and the adjacent transparent electrode is at least partly
formed to have a width of not more than 3 .mu.m, thereby reducing
the inter-pixel region that does not contribute to display. Namely,
it is possible to attain a high aperture ratio in a liquid crystal
display panel using the above-described active matrix
substrate.
[0134] Further, the active matrix substrate of the present
invention is preferably arranged so that the reflective electrode
does not cover source wiring, when viewed in the normal direction
of the display surface of the active matrix substrate.
[0135] Conventionally, gate wiring and source wiring are located in
the inter-pixel region on the active matrix substrate. In the
arrangement where the inter-pixel region is reduced by closely
locating the boundary of the reflection region and the boundary of
the transmission region, as in the present invention, the
reflective electrode covers at least part of either gate wiring or
source wiring.
[0136] With the above-mentioned arrangement, the reflective
electrode is arranged so as not to cover source wiring, thereby
reducing the parasitic capacitance between the source wiring and
the reflective electrode. This consequently reduces the crosstalk
(shadow) caused by the capacitive coupling of the source wiring and
the reflective electrode.
[0137] Further, the active matrix substrate of the present
invention may be so arranged that the reflective electrode covers
at least part of gate wiring, when viewed in the normal direction
of the display surface of the active matrix substrate, and the
reflective electrode covers gate wiring different from gate wiring
that drives a pixel of the reflective electrode.
[0138] In an arrangement where the reflective electrode covers at
least part of gate wiring, if the reflective electrode covers the
gate bus line that drives the pixel of the reflective electrode in
question, the parasitic capacitance between the reflective
electrode and the gate wiring increases. This accordingly increases
a change in a pixel potential when the gate signal falls after
writing, causing a problem such as a display defect.
[0139] In contrast, in the above-mentioned arrangement, each
reflective electrode is arranged so as to cover gate wiring
different from gate wiring that drives the pixel of the reflective
electrode in question, thereby obviating the above problem.
[0140] Further, the active matrix substrate of the present
invention, used for a liquid crystal display device of the normally
white mode, is preferably arranged so as to include a
light-shielding layer located corresponding to a blank region that
is neither the reflection region nor the transmission region.
[0141] With the active matrix substrate as arranged above, the
inter-pixel region exists between the transparent electrodes and
between the reflective electrodes. Thus, at a portion where the
inter-pixel region between the transmission regions and the
inter-pixel region between the reflection regions cross, a certain
area of blank region arises, to which neither the transparent
electrode nor the reflective electrode can apply a voltage.
[0142] The blank region always shows white display in the normally
white mode, thus causing contrast decrease. However, with the
above-mentioned arrangement, a light-shielding layer is provided
corresponding to the blank region, thereby preventing the contrast
decrease.
[0143] Further, a liquid crystal display panel of a transflective
type of the present invention is so arranged that the
above-described active matrix substrate and a counter substrate
sandwich a liquid crystal layer.
[0144] Further, a liquid crystal display device of a transflective
type of the present invention is provided with the above-described
liquid crystal display panel.
[0145] In the above-arranged liquid crystal display panel of the
transflective type and the liquid crystal display device of the
transflective type, as in the above-described active matrix
substrate, it is possible to reduce a ratio of the inter-pixel
region, which does not contribute to display, with respect to the
entire display screen, thereby achieving a high aperture ratio.
[0146] The invention being thus described, it will be obvious that
the same may be varied in many ways. Such variations are not to be
regarded as a departure from the spirit and scope of the invention,
and all such modifications as would be obvious to one skilled in
the art are intended to be included within the scope of the
following claims.
* * * * *